From homoligand- to mixed-ligand- monolayer-protected metal nanoparticles: A scanning tunneling microscopy investigation

Alicia M. Jackson, Ying Hu, Paulo Jacob Silva, Francesco Stellacci

Research output: Contribution to journalArticle

Abstract

The ligand shell that coats, protects, and imparts a large number of properties to gold nanoparticles is a 2-D self-assembled monolayer wrapped around a 3-D metallic core. Here we present a study of the molecular packing of ligand shells on gold nanoparticles based on the analysis of scanning tunneling microscopy (STM) images. We discuss methods for optimal nanoparticle sample preparation in relation to STM imaging conditions. We show that the packing of a self-assembled monolayer composed solely of octanethiols on gold nanoparticles depends on the particle's diameter with an average headgroup spacing of 5.4 Å, which is different from that of similar monolayers formed on flat Au(111) surfaces (5.0 Å). In the case of nanoparticles coated with mixtures of ligands-known to phase separate into randomly shaped and ordered domains on flat surfaces-we find that phase separation leads to the formation of concentric, ribbonlike domains of alternating composition. The spacing of these domains depends on the ligand shell composition. We find that, for a given composition, the spacing increases with diameter in a manner characterized by discontinuous transitions at "critical" particle sizes. We discuss possible interpretations for the observed trends in our data.

Original languageEnglish
Pages (from-to)11135-11149
Number of pages15
JournalJournal of the American Chemical Society
Volume128
Issue number34
DOIs
Publication statusPublished - Aug 30 2006

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ASJC Scopus subject areas

  • Chemistry(all)

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